High-Temperature Mechanical Performance and Microstructural Development in Nickel-Based Alloy 617 Diffusion Bonds for High-Efficiency Heat Exchangers

Abstract Microchannel heat exchanger technology is being developed for next-generation concentrating solar power (CSP) systems to enable primary supercritical CO2 (sCO2) power cycle heat addition. The economic viability of these plants hinges on a high-efficiency heat exchanger that can last 30 years, resisting creep, fatigue, corrosion, and erosion, while also handling thermal cycling. However, the longevity and operational limits of microchannel heat exchangers, especially those made from high-nickel alloys, remain unclear in part because the long-term performance of the diffusion bonds is not well characterized. These compact heat exchangers are constructed by diffusion bonding of thin metallic etched sheets, where grains of the base material grow across sheet interfaces under high temperatures and pressures. This manuscript explores the use of Inconel® alloy 617 (IN617) in manufacturing diffusion-bonded heat exchangers, focusing on the mechanical properties of IN617 diffusion-bonded test blocks subjected to tensile, creep, and fatigue testing. Ongoing pre- and post-test material characterization aims to identify key microstructural features of IN617 diffusion bonds, quantify grain growth, and understand potential high-temperature damage modes that could affect component performance. This effort provides critical materials data to enable improved lifetime prediction of CSP heat exchangers and ensure quality control in the manufacturing of high-temperature diffusion bonds for advanced power cycle applications such as sCO2 turbomachinery.